Procedures for introducing stents and stent-grafts

ABSTRACT

The present invention relates to a process for deploying a folded stent or stent-graft in a lumen. The stent or stent graft is maintained in the folded configuration by a slip line that is attached to the folded stent or stent-graft, along a longitudinal fold edge. The folded stent or stent-graft is inserted into a lumen and the slip line is axially moved along a longitudinal line to allow the folded stent or stent-graft to expand to its enlarged, deployed configuration.

This is a divisional application of application Ser. No. 08/754,398,filed Nov. 20, 1996, which is a continuation of application Ser. No.08/361,793, filed Dec. 21, 1994, which in turn is a continuation-in-partof application Ser. No. 08/303,060, filed Sep. 8, 1994, each of which isnow abandoned.

FIELD OF THE INVENTION

This invention is a medical device and a method of using it. The deviceis a foldable stent or stent-graft which may be percutaneously deliveredwith (or on) a catheter, typically an endovascular catheter, to a bodycavity or lumen and then expanded. It may also be delivered or viasurgical (or other) techniques. The expandable stent structure utilizestorsional members which distribute bending and folding loads in such away that the stent is not plastically deformed. The stent'sconfiguration allows it to be folded or otherwise compressed to a verysmall diameter prior to deployment without changing the length of thestent. The graft component cooperating with the stent is tubular andpreferably is blood-compatible material which may, if desired, bereinforced with fibers. The stent is able to provide collapsible supportfor otherwise frangible graft material.

The invention also involves procedures for folding stents and fordeploying stents or stent-grafts which have been folded, bound, orotherwise collapsed to significantly smaller diameters for insertioninto a human or animal body. When used with super-elastic alloys, thestent may be collapsed at a convenient temperature either above or,preferably, below the transition temperature of the alloy. Thedeployment procedures may involve the use of an outer sleeve to maintainthe stent or stent-graft at a reduced diameter or may involve one ormore external or internal "slip-lines" or "tether wires" to hold andthen to release the device.

BACKGROUND OF THE INVENTION

Treatment or isolation of vascular aneurysms or of vessel walls whichhave been thinned or thickened by disease has traditionally been donevia surgical bypassing with vascular grafts. Shortcomings of thisprocedure include the morbidity and mortality associated with surgery,long recovery times after surgery, and the high incidence of repeatintervention needed due to limitations of the graft or of the procedure.Vessels thickened by disease are currently sometimes treated lessinvasively with intraluminal stents that mechanically hold these vesselsopen either subsequent to or as an adjunct to a balloon angioplastyprocedure. Shortcomings of current stents include the use of highlythrombogenic materials (stainless steels, tantalum, ELGILOY) which areexposed to blood, the general failure of these materials to attract andsupport functional endothelium, the irregular stent/vessel surface thatcauses unnatural blood flow patterns, and the mismatch of compliance andflexibility between the vessel and the stent.

Important to this invention is the use of less invasive intraluminaldelivery and, desirably, placement of a nonthrombogenic blood-carryingconduit having a smooth inner lumen which will endothelize. Onedesirable biologic material for the inner layer of the inventivestent-graft is collagen-based and, although it will fold with ease, isotherwise fairly frangible or inelastic in that it has very littleability to stretch. Mounting a collagen tube on the outside of or as apart of a balloon-expandable stent will usually cause the tube to tear.Mounting such a tube on the inside of a balloon expandable stent willyield a torn irregular surface exposed to blood flow. Further, balloonexpandable devices that rely upon plastic deformation of the stent toachieve a deployed shape are subject to abrupt closure as a result oftrauma when the devices are placed in a vessel near the skin surface oracross a joint or ligament. Those self-expanding stents which rely onthe shortening of the stent upon radial expansion at deployment maycause vessel tearing problems similar to those observed with the use ofballoon expandable devices. Obviously, stents which shorten duringdeployment are also subject to deployment placement inaccuracies.

The most desired variations of this invention involve a stent-graftwhich is self-expanding, which does not shorten upon delivery, which hasexcellent longitudinal flexibility, which has high radial compliance tothe vessel lumen, and exposes the blood to a smooth, nonthrombogenicsurface often capable of supporting endothelium growth.

The inventive device may be delivered in a reduced diameter and expandedto maintain the patency of any conduit or lumen in the body. An area inwhich the inventive stent and stent graft is particularly beneficial isin the scaffolding of atherosclerotic lesions in the cardiovascularsystem to establish vessel patency, prevention of thrombosis, and thefurther prevention of restenosis after angioplasty. In contrast to manyof the stents discussed below having metallic struts intruding into theblood flow in the vessel lumen which generate turbulence and createblood stasis points initiating thrombus formation, the smooth,continuous surface provided by the preferred tubular collagen-basedinner conduit of our invention provides a hemodynamically superiorsurface for blood flow.

Clearly the stent and stent-graft may also be employed in any bodycavity, opening, or lumen where a device such as is described here isappropriate.

The absence of gaps or holes in the graft structure between stent strutsof our invention allows the tacking of both large and small flaps andtears in the vessel wall. These flaps disrupt blood flow and attractthrombus. The disruption of the natural anti-thrombotic covering ofendothelium only worsens the condition. When collagen-based materialsare used, the collagen-based barrier interposed between blood and adisrupted or injured portion of the vessel wall serves to mask injuredintimal or medial layers from blood, thereby preventing thrombusformation and intimal proliferation which may lead to restenosis.

The stent-graft acts as a mechanical barrier preventing tissue fromproliferating into or impinging the lumen. The nature of the bioactivityof the collagen and the smoother flow characteristics at theblood-contacting surface are conducive to endothelial cell attachmentand growth thereby assuring the long-term blood compatibility of thedevice.

Mechanically, the preferred stent structures (described in U.S. patentapplication Ser. Nos. 08/221,815 and 08/222,263 both filed on Apr. 1,1994 by Lau et al, the entirety of which are incorporated by reference)provide a good combination of radial strength and flexibility. Thepreferred stent structures are also radially resilient and may becompletely crushed or flattened and yet spring open again once theobstructive loading is removed. This ability is important for use inexposed portions of the body around the peripheral vasculature or aroundjoints. The stent-graft can sustain a crushing traumatic blow orcompression from the bending of a joint and still return to the openconfiguration once the load is removed.

With regard to delivery, the inventive self-expansion mechanism andprocedure eliminates the need for a balloon catheter and the associatedballoon rupture problems often associated with balloons. In addition,the absence of the bulk of the balloon allows a smaller delivery profileto be achieved. Unlike some other self-expanding stent designs, thisstent-graft maintains a constant length throughout the expansionprocess. Thus, the stent-graft would not have some of the positioningproblems associated with other many self-expanding stents. In treatinglonger lesions, our self-expanding design eliminates the need forspecial long balloons or repositioning of the balloon between inflationsin order to expand the entire length of the stent.

Stents

The stents currently described in the open literature include a widevariety of different shapes.

Wallsten, U.S. Pat. No. 4,655,771, suggests a vascular prosthesis fortransluminal implantation which is made up of a flexible tubular bodyhaving a diameter that is varied by adjusting the axial separation ofthe two ends of the body relative to each other. In general, the bodyappears to be a woven device produced of various plastics or stainlesssteel.

U.S. Pat. No. 4,760,849, to Kroph, shows the use of a ladder-shaped coilspring which additionally may be used as a filter in certain situations.

Porter, U.S. Pat. No. 5,064,435, suggests a stent made up of two or moretubular stent segments which may be deployed together so to produce asingle axial length by a provision of overlapping areas. This concept isto permit the use of segments of known length, which, when deployed, maybe used together in overlapping fashion additively to provide a stent ofsignificant length.

Quan-Gett, U.S. Pat. No. 5,151,105, discloses an implantable,collapsible tubular sleeve apparently of an outer band and an innerspring used to maintain the sleeve in a deployed condition.

Wall, U.S. Pat. No. 5,192,307, suggests a stent having a number of holestherein and which is expandable using an angioplasty balloon so to allowratchet devices or ledges to hold the stent in an open position once itis deployed.

Gianturco, in U.S. Pat. Nos. 4,580,568 and 5,035,706, describes stentsformed of stainless steel wire arranged in a closed zigzag pattern. Thestents are compressible to a reduced diameter for insertion into andremoval from a body passageway. The stents appear to be introduced intothe selected sites by discharge of the collapsed zigzag wireconfiguration from the tip of a catheter.

U.S. Pat. Nos. 4,830,003 and 5,104,404, to Wolff et al., shows a stentof a zigzag wire configuration very similar in overall impression to theGianturco device. However, the stent is said to be self-expanding andtherefore does not need the angioplasty balloon for its expansion.

Hillstead, U.S. Pat. 4,856,516, suggests a stent for reinforcing vesselwalls made from a single elongated wire. The stent produced iscylindrical and is made up of a series of rings which are, in turn,linked together by half-hitch junctions produced from the singleelongated wire.

Wiktor, U.S. Pat. Nos. 4,649,992, 4,886,062, 4,969,458, and 5,133,732,shows wire stent designs using variously a zigzag design or, in the caseof Wiktor '458, a helix which winds back upon itself. Wiktor '062suggests use of a wire component made of a low-memory metal such ascopper, titanium or gold. These stents are to be implanted using aballoon and expanded radially for plastic deformation of the metal.

Wiktor '458 is similarly made of low-memory alloy and is to beplastically deformed upon its expansion on an angioplasty balloon.

Wiktor '732 teaches the use of a longitudinal wire welded to each turnof the helically wound zig-zag wire which is said to prevent thelongitudinal expansion of the stent during deployment. A furthervariation of the described stent includes a hook in each turn of thehelix which loops over a turn in an adjacent turn.

WO93/13825, to Maeda et al, shows a self-expanding stent similar to theGianturco, Wolff, and Wiktor designs, formed of stainless steel wire,which is built into an elongated zig-zag pattern, and helically woundabout a central axis to form a tubular shape interconnected with afilament. The bends of the helix each have small loops or "eyes" attheir apexes which are inter-connected with a filament. Because of theteaching to connect the eyes of the apexes, the stent appears to be adesign that axially expands during compression and may tear attachedgrafts because of the relative change in position of the arms of thezig-zag during compression of the stent.

MacGregor, U.S. Pat. No. 5,015,253, shows a tubular non-woven stent madeup of a pair of helical members which appear to be wound using opposite"handedness". The stent helices desirably are joined or secured at thevarious points where they cross.

Pinchuk, in U.S. Pat. Nos. 5,019,090, 5,092,877, and 5,163,958, suggestsa spring stent which appears to circumferentially and helically windabout as it is finally deployed except, perhaps, at the very end link ofthe stent. The Pinchuk '958 patent further suggests the use of apyrolytic carbon layer on the surface of the stent to present a poroussurface of improved antithrombogenic properties. The helices are notlinked to each other, however, nor is there any suggestion that thehelices be maintained in a specific relationship either as deployed oras kept in the catheter prior to deployment.

U.S. Pat. No. 5,123,917, to Lee, suggests an expandable vascular grafthaving a flexible cylindrical inner tubing and a number of "scaffoldmembers" which are expandable, ring-like, and provide circumferentialrigidity to the graft. The scaffold members are deployed by deformingthem beyond their plastic limit using, e.g., an angioplasty balloon.

Tower, in U.S. Pat. Nos. 5,161,547 and 5,217,483, shows a stent formedfrom a zig-zag wire wound around a mandrel in a cylindrical fashion. Itis said to be made from "a soft platinum wire which has been fullyannealed to remove as much spring memory as possible." A longitudinalwire is welded along the helically wound sections much in the same wayas was the device of Wiktor.

There are a variety of disclosures in which super-elastic alloys such asnitinol are used in stents. See, U.S. Pat. Nos. 4,503,569, to Dotter;4,512,338, to Balko et al.; 4,990,155, to Wilkoff; 5,037,427, to Harada,et al.; 5,147,370, to MacNamara et al.; 5,211,658, to Clouse; and5,221,261, to Termin et al. None of these references suggest a devicehaving discrete, individual, energy-storing torsional members as arerequired by this invention.

Jervis, in U.S. Pat. Nos. 4,665,906 and 5,067,957, describes the use ofshape memory alloys having stress-induced martensite properties inmedical devices which are implantable or, at least, introduced into thehuman body.

Stent-Grafts

A variety of stent-graft designs are shown in the following literature.

Perhaps the most widely known such device is shown in Ersek, U.S. Pat.No. 3,657,744. Ersek shows a system for deploying expandable,plastically deformable stents of metal mesh having an attached graftthrough the use of an expansion tool.

Palmaz describes a variety of expandable intraluminal vascular grafts ina sequence of patents: U.S. Pat. Nos. 4,733,665; 4,739,762; 4,776,337;and 5,102,417. The Palmaz '665 patent suggests grafts (which alsofunction as stents) that are expanded using angioplasty balloons. Thegrafts are variously a wire mesh tube or of a plurality of thin barsfixedly secured to each other. The devices are installed, e.g., using anangioplasty balloon and consequently are not seen to be self-expanding.

The Palmaz '762 and '337 patents appear to suggest the use ofthin-walled, biologically inert materials on the outer periphery of theearlier-described stents.

Finally, the Palmaz '417 patent describes the use of multiple stentsections each flexibly connected to its neighbor.

Rhodes, U.S. Pat. No. 5,122,154, shows an expandable stent-graft made tobe expanded using a balloon catheter. The stent is a sequence ofring-like members formed of links spaced apart along the graft. Thegraft is a sleeve of a material such as expanded a polyfluorocarbon,e.g., GORETEX or IMPRAGRAFT.

Schatz, U.S. Pat. No. 5,195,984, shows an expandable intraluminal stentand graft related in concept to the Palmaz patents discussed above.Schatz discusses, in addition, the use of flexibly-connecting vasculargrafts which contain several of the Palmaz stent rings to allowflexibility of the overall structure in following curving body lumen.

Cragg, "Percutaneous Femoropopliteal Graft Placement", Radiology, vol.187, no. 3, pp. 643-648 (1993), shows a stent-graft of a self-expanding,nitinol, zig-zag, helically wound stent having a section ofpolytetrafluoroethylene tubing sewed to the interior of the stent.

Cragg (European Patent Application 0,556,850) discloses an intraluminalstent made up of a continuous helix of zig-zag wire and having loops ateach apex of the zig-zags. Those loops on the adjacent apexes areindividually tied together to form diamond-shaped openings among thewires. The stent may be made of a metal such as nitinol (col. 3, lines15-25 and col. 4, lines 42+) and may be associated with a"polytetrafluoroethylene (PTFE), dacron, or any other suitablebiocompatible-material". Those biocompatible materials may be inside thestent (col. 3, lines 52+) or outside the stent (col. 4, lines 6+). Thealignment of the wire and the way in which it is tied mandates that itexpand in length as it is expanded from its compressed form.

Grafts

As was noted above, the use of grafts in alleviating a variety ofvascular conditions is well known. Included in such known graftingdesigns and procedures are the following.

Medell, U.S. Pat. No. 3,479,670, discloses a tubular prothesis adaptedto be placed permanently in the human body. It is made of framework orsupport of a synthetic fiber such as DACRON or TEFLON. The tube is saidto be made more resistant to collapse by fusing a helix of apolypropylene monofilament to its exterior. The reinforced fabric tubeis then coated with a layer of collagen or gelatin to render the tubing(to be used as an esophageal graft) impermeable to bacteria or fluids.

Sparks, in U.S. Pat. Nos. 3,514,791, 3,625,198, 3,710,777, 3,866,247,and 3,866,609, teach procedures for the production of various graftstructures using dies of suitable shape and a cloth reinforcing materialwithin the die. The die and reinforcement are used to grow a graftstructure using a patient's own tissues. The die is implanted within thehuman body for a period of time to allow the graft to be produced. Thegraft is in harvested and implanted in another site in the patient'sbody by a second surgical procedure.

Braun, in U.S. Pat. No. 3,562,820, shows a biological prosthesismanufactured by applying onto a support of a biological tissue (such asserosa taken from cattle intestine) a collagen fiber paste. Theprocedure is repeated using multiple layers of biological tissue andcollagen fiber paste until a multi-layer structure of the desired wallthicknesses is produced. The prosthesis is then dried and removed priorto use.

Dardik et al, U.S. Pat. No. 3,974,526, shows a procedure for producingtubular prostheses for use in vascular reconstructive surgeries. Theprosthesis is made from the umbilical cord of a newly born infant. It iswashed with a solution of 1 percent hydrogen peroxide and rinsed withRinger's lactate solution. It is then immersed in a hyaluronidasesolution to dissolve the hyaluronic acid coating found in the umbilicalcord. The vessels are then separated from the cord and their naturalinterior valving removed by use of a tapered mandrel. The vessels arethen tanned with glutaraldehyde. A polyester mesh support is applied tothe graft for added support and strength.

Whalen, U.S. Pat. No. 4,130,904, shows a prosthetic blood conduit havingtwo concentrically associated tubes with a helical spring between them.Curved sections in the tube walls help prevent kinking of the tube.

Ketharanathan, U.S. Pat. No. 4,319,363, shows a procedure for producinga vascular prosthesis suitable for use as a surgical graft. Theprosthesis is produced by implanting a rod or tube in a living host andallowing collagenous tissue to grow on the rod or tube in the form ofcoherent tubular wall. The collagenous implant is removed from the rodor tube and tanned in glutaraldehyde. The prosthesis is then ready foruse.

Bell, U.S. Pat. No. 4,546,500, teaches a method for making a vesselprosthesis by incorporating a contractile agent such as smooth musclecells or platelets into a collagen lattice and contracting the latticearound a inner core. After the structure has set, additional layers areapplied in a similar fashion. A plastic mesh sleeve is desirablysandwiched between the layers or imbedded within the structure toprovide some measure of elasticity.

Hoffman Jr. et al, U.S. Pat. No. 4,842,575, shows a collagen impregnatedsynthetic vascular graft. It is made of a synthetic graft substrate anda cross-linked collagen fibril. It is formed by depositing a aqueousslurry of collagen fibrils into the lumen of the graft and massaging theslurry into the pore structure of the substrate to assure intimateadmixture in the interior. Repeated applications and massaging anddrying is said further to reduce the porosity of the graft.

Alonoso, U.S. Pat. No. 5,037,377, is similar in overall content to theHoffman Jr. et al patent discussed above except that, in addition tocollagen fibers, soluble collagen is introduced into the fabric. Asuitable cross-linking agent such as glutaraldehyde is used to bondadjacent collagen fibers to each other.

Slepian et al, U.S. Pat. No. 5,213,580, teaches a process described as"paving" or "stabilizing by sealing the interior surface of a bodyvessel or organ" by applying a biodegradable polymer such as apolycaprolactone. The polymer is made into a tubular substrate, placedin position, and patched into place.

Finally, there are known vascular grafts using collagenous tissue withreinforcing structure. For instance, Pinchuk, in U.S. Pat. Nos.4,629,458 and 4,798,606, suggests the use of collagen with some othertype of fibrous structure supporting the collagen as a biograft.Similarly, Sinofsky et al., U.S. Pat. No. 5,100,429, suggests apartially-cured, collagen-based material used to form a graft within ablood vessel.

Kreamer, U.S. Pat. No. 4,740,207, suggests a intraluminal graft made ofa semi-rigid resilient tube, open along a seam extending from one end tothe other, which is expanded within the vessel and which resultinglarger diameter is maintained by use of a ledge at the longitudinal seamfor catching the opposite side of the seam on the expanded graft.

Deployment Procedures

Since most stents are introduced into the human body and deployed usingan angioplasty balloon, there is very little description of themethodology or devices used in deploying self-expanding stents in stentgrafts. A typical example of such expandable stents and methods ofimplant is shown in Wiktor, U.S. Pat. No. 4,886,062, in which a lowmemory alloy such as specified stainless steels, titanium alloys, or19-22 karat gold is deployed using a balloon.

More pertinent to the invention here are the deployment devices shown intwo patents to Hillstead (U.S. Pat. Nos. 4,913,141 and 5,019,085). Thesepatents show a stent delivery system in which a delivery catheter havinga cylindrical wall is wrapped with a stent. The stent is one which isexpandable upon release. At each end of the stent is a loop whichengages a release wire extending from within the catheter. The releasewire extends from one end of the stent to the other. By pulling therelease wire through the interior of the deployment catheter, the distalend is first released, and upon further pulling the second end isreleased from the exterior of the catheter. The deployment catheter maythen be removed from the interior of the vessel.

None of the cited references suggest the claimed procedures and devices.

SUMMARY OF THE INVENTION

This invention involves procedures for folding and also for deliveringfoldable stents or stent-grafts to a site within the human body. Thedelivery may be percutaneous and through or over an endovascularcatheter or via use of an endoscopic device through a body opening orvia the use of surgical or other procedures. The preferred expandablestent structure utilizes torsional regions which allow it to be foldedto a very small diameter prior to deployment. In some variations of thepreferred stent structure, the torsional members have an undulatingshape which may be helically deployed to form the stent's cylindricalshape. The undulating shape may be aligned to allow the shapes inadjacent turns of the helix to be in phase. The undulating shapes may begenerally V-shaped, U-shaped, sinusoidal, or ovoid. Adjacent undulatingshapes may be held in the phased relationship using a flexible linkage,often made of a polymeric material. The undulating torsional members donot have any means at (or near) the apex of the undulating shapes whichwould tend to constrict the movement of the flexible linkage duringcompression or bending of the stent. The stent is preferably made of ahighly flexible, superelastic alloy such as nitinol, but may be of anysuitable elastic material such as various of the medically acceptedstainless steels. The stent structure may also be of a series of ringsincorporating the torsional members, which rings may be axially linked.

The graft component used to complement the stent is tubular and may bemade of a polymeric material which may, if desired, be reinforced withfibers of random, woven, roving, or wound configurations. The tubularmember may be cast onto or otherwise attached or imbedded into or ontothe stent structure. The stent-graft may be used to reinforce vascularirregularities and provide a smooth interior vascular surface,particularly within smaller vessels. Obviously the stent and stent-graftmay be used in any other medical service where such devices are commonlyemployed.

The device used in deploying the stent or stent grafts employs one ormore "slip lines" which, in turn, may be of any of a variety of forms.The slip lines may be threaded through the stent, through loopsspecifically included in the folded stent for this purpose; the sliplines may be direct or may be woven in such a way that they act as would"sack knots" in releasing the stent as the lines are unwoven.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, and 1E are plan views of an unrolled stent formsuitable for use in the invention.

FIG. 2 is a side view of the a stent as shown in FIGS. 1A-1E.

FIG. 3 is a close-up of a portion of the stent shown in FIG. 2.

FIG. 4 is an abstracted portion of a suitable stent and shows theconcept of torsion on a portion of that stent.

FIG. 5 is a side view of the inventive stent showing a variation havingflared ends.

FIGS. 6, 7, and 8 show plan views of an unrolled stent produced fromflat stock.

FIG. 9 shows a quarter view of the rolled stent using the flat stockpattern shown in FIG. 7.

FIG. 10 shows a plan view of an unrolled stent produced from flat stockhaving a ringed structure.

FIG. 11 shows a front quarter view of the rolled ring structured stentusing the flat stock pattern shown in FIG. 9.

FIGS. 12, 13, and 14 show plan views of variations of unrolled stentsuseful in this invention.

FIGS. 15A, 15C, and 15E show procedures for folding the stent-grafts.FIGS. 15B, 15D, and 15F show the corresponding folded stent-grafts.

FIGS. 16A-16C show a schematic procedure for deploying the stent-graftsusing an external sleeve.

FIGS. 17A and 18A show front quarter views of folded stents orstent-grafts held in that folded position by a tether wire. FIGS. 17B,17C, 18B, and 18C show end views of the folded stent and of the openstent shown respectively in FIGS. 17A and 18A.

FIGS. 19A-19C show a schematic procedure for deploying the stent-grafts(as shown in FIGS. 17A-17C and 18A-18C) using a tether wire.

FIG. 20 shows a close-up view of a stent fold line using a preferredsack knot in the slip line.

FIGS. 21 and 22 show front quarter views of folded stents orstent-grafts held in that folded position by a tether wire using a sackknot.

DESCRIPTION OF THE INVENTION

As was noted above, this invention is a procedure for the folding anddeployment of an expandable stent, a stent-graft, or a fiber- orfilament-reinforced stent-graft. Also included in the invention is astent or stent graft in combination with a slip-line. The stent-graftmay be a combination of several components: a thin-walled tube generallycoaxial with the stent, the expandable stent structure, and an optionalnetwork of fibers used to reinforce the tubular component. Theexpandable stent structure may be a cylindrical body produced of ahelically placed (wound or otherwise preformed) torsion member having anundulating or serpentine shape or a series of axially situated ringscomprising those torsion members. When the undulating torsion member isformed into the cylinder, the undulations may be aligned so that theyare "in phase" with each other. The undulations are desirably linked,typically with a flexible linkage of a suitable polymeric or metallicmaterial, to maintain the phased relationship of the undulations duringcompression and deployment. These stent configurations are exceptionallykink-resistant and flexible, particularly when flexed along thelongitudinal axis of the stent.

When the stent is used in a reinforced stent-graft, that is to say: thestent is included into a thin-walled tube having reinforcing fibers, thefibers (or threads or filaments) may be formed into a network, such as atubular mesh or otherwise reinforced with fibers of random, woven,roving, or wound configurations. The stent-graft may be delivered(perhaps, percutaneously through the vasculature) after having beenfolded to a reduced diameter. Once reaching the intended delivery site,it is expanded to form a lining on the vessel wall or cavity.

Methods of delivering the various devices using, among other devices, apercutaneous catheter and a slip line are also an aspect of theinvention.

Stent Component

The materials typically used for vascular grafts, e.g.,polytetrafluoroethylene (PTFE), collagen, etc. usually do not have thestiffness or strength by themselves both to stay open against the radialinward loads found in those vessels and to prevent their slippage fromthe chosen deployment site. In order to provide the strength required, aradially rigid stent structure may be incorporated into the stent-graft.The stent may be constructed of a reasonably high strength material,i.e., one which is resistant to plastic deformation when stressed. Thestructure is typically from one of three sources: 1.) a wire form inwhich a wire is first formed into an undulating shape and the resultingundulating shape is helically wound to form a cylinder, 2.) anappropriate shape is formed from a flat stock and wound into a cylinder,and 3.) a length of tubing is formed into an appropriate shape. Thesestent structures are typically oriented coaxially with the tubular graftcomponent. The stent structures may be placed on the outer surface orthe inner surface of the tubular member although it is often desirablethat the stent be imbedded in the graft tubing wall for ease ofintegration with the tubing and to prevent the stent's exposure toblood. It is desired that the stent structure have the strength andflexibility to tack the graft tubing firmly and conformally against thevessel wall. In order to minimize the wall thickness of the stent-graft,the stent material should have a high strength-to-volume ratio. Use ofdesigns described herein provides stents which are shorter in lengththan those often used in the prior art. Additionally, the designs do notsuffer from a tendency to twist (or helically unwind) or to shorten asthe stent is deployed. As will be discussed below, materials suitable inthese stents and meeting these criteria include various metals and somepolymers.

A stent-graft, whether percutaneously delivered with a catheter ordelivered using surgical techniques, must expand from a reduceddiameter, necessary for delivery, to a larger deployed diameter. Thedeployed diameters of these devices obviously vary with the size of thebody lumen or cavity into which they are placed. For instance, thestents of this invention may range in size (for neurologicalapplications) from 2.0 mm in diameter to 30 mm in diameter (forplacement in the aorta). A range of about 2.0 mm to 6.5 mm (perhaps to10.0 mm) is believed to be desirable. Typically, expansion ratios of 2:1or more are required. These stents are capable of expansion ratios of upto 5:1 for larger diameter stents. Typical expansion ratios for use withthe stents and stent-grafts of the invention typically are in the rangeof about 2:1 to about 4:1 although the invention is not so limited. Thethickness of the stent-materials obviously varies with the size (ordiameter) of the stent and the ultimate required yield strength of thefolded stent. These values are further dependent upon the selectedmaterials of construction. Wire used in these variations are typicallyof stronger alloys, e.g., nitinol and stronger spring stainless steels,and have diameters of about 0.002 inches to 0.005 inches. For the largerstents, the appropriate diameter for the stent wire may be somewhatlarger, e.g., 0.005 to 0.020 inches. For flat stock metallic stents,thicknesses of about 0.002 inches to 0.005 inches is usually sufficient.For the larger stents, the appropriate thickness for the stent flatstock may be somewhat thicker, e.g., 0.005 to 0.020 inches.

The stent-graft is fabricated in the expanded configuration. In order toreduce its diameter for delivery the stent-graft would be folded alongits length, similar to the way in which a PCTA balloon would be folded.It is desirable, when using super-elastic alloys which are also havetemperature-memory characteristics, to reduce the diameter of the stentat a temperature below the transition-temperature of the alloys. Oftenthe phase of the alloy at the lower temperature is somewhat moreworkable and easily formed. The temperature of deployment is desirablyabove the transition temperature to allow use of the super-elasticproperties of the alloy.

As a generic explanation of the mechanical theory of the inventivestent, reference is made to FIGS. 1A, 1B, 1C, 1D, 1E, 2, 3, and 4. FIG.1A is a plan view of an isolated section of a stent device suitable foruse in the invention and is intended both to identify a suitable stentvariation and to provide conventions for naming the components of thetorsion member (100). FIG. 1A shows, in plan view, an undulating torsionmember (100) formed from a wire stock into a U-shape. A torsion pair(102) is made up of an end member (104) and two adjacent torsion lengths(106). Typically, then, each torsion length (106) will be a component toeach of its adjacent torsion pairs (102). The U-shaped torsion pair(102) may be characterized by the fact that the adjacent torsion lengthsare generally parallel to each other prior to formation into the stent.

The depicted stents use undulating torsion members which are "open" or"unconfined" at their apex or end member (104). By "open" or"unconfined" is meant that the apex or end member (104) does not haveany means in that apex which would tend to inhibit the movement of theflexible linkage (discussed below) down between the arms or torsionlengths (106) of the torsion pair (102).

FIG. 1B shows another variation of the stent having a sinusoidal shapedtorsion member (108). In this variation, the adjacent torsion lengths(110) are not parallel and the wire forms an approximate sine shapebefore being formed into a cylinder.

FIG. 1C shows a variation having an ovoid shaped torsion member (112).In this variation, the adjacent torsion lengths (114) are again notparallel. The wire forms an approximate open-ended oval with eachtorsion pair (116) before being formed into a cylinder.

FIG. 1D shows another variation having a V-shaped torsion member (118).In this variation, the adjacent torsion lengths (120) form a relativelysharp angle at the torsion end (122) shape before being formed into acylinder.

FIG. 1E shows a variation in which adjacent torsion members on the stent(117) have differing amplitude. The peaks of the high amplitude torsionmembers (119) may be lined up "out of phase" or "peak to peak" withshort amplitude (121) or high amplitude torsion members in the adjacentturn of the helix or may be positioned "in phase" similar to thosediscussed with regard to FIG. 2 below.

The configurations shown in FIGS. 1A-1E are exceptionally kink-resistantand flexible when flexed along the longitudinal axis of the stent.

As ultimately deployed, a section of the torsion member found on one ofFIGS. 1A-1E would be helically wound about a form of an appropriate sizeso that the end members (egg., 104 in FIG. 1A) would be centered betweenthe end members of the torsion member on an adjacent turn of the helix.This is said to be "in phase". "Out of phase" would be the instance inwhich the adjacent members meet directly, i.e., end member-to-endmember. In any event, once so aligned, the phasic relationship may bestabilized by weaving a flexible linkage through the end members fromone turn of the helix to the next.

FIG. 2 shows a side view of a typical stent (122) made according to thisinvention including the phased relationship of the helical turns of thestent and the flexible linkage (124).

FIG. 3 shows a close-up of the FIG. 2 stent and depicts the phasedrelationship (within box A) and shows in detail a typical way in whichthe flexible linkage (124) is looped through the various end members(104) to maintain the phased relationship. It may be noted that theflexible linkage (124) is free to move away from the apex at the endmembers (104) without constraint.

The stent may be folded in some fashion (as will be discussed below) fordeployment. During the step of folding, the stent undergoes atransformation. FIG. 4 shows an isolated torsion pair (102). When thetorsion pair (102) undergoes a flexing in the amount of α°, the endmember will flex some amount β°, torsion length (130) will undertake atwist of γ°, and torsion length (132) will undertake a twist opposite ofthat found in torsion length (130) in the amount of δ°. The amounts ofangular torsion found in the torsion lengths (130 and 132) will notnecessarily be equal because the torsion lengths are not necessarily atthe same angle to the longitudinal axis of the stent. Nevertheless, thesum of β°+γ°+δ° will equal α°. When a value of α° is chosen, as byselection of the shape and size of the stent upon folding, the values ofthe other three angles (β°,γ°,δ°) are chosen by virtue of selection ofnumber of torsion pairs around the stent, size and physicalcharacteristics of the wire, and length of the torsion lengths (103 and132). Each of the noted angles must not be so large as to exceed thevalues at which the chosen material of construction plastically deformsat the chosen value of α°.

To further explain: it should understood that the torsion pair (102)undergoes a significant of flexing as the stent is folded or compressedin some fashion. The flexing provides a twist to the torsion lengths(103 and 132), a significant portion of which is generally parallel tothe longitudinal axis of the stent. It is this significant imposedlongitudinal torsion which forms an important concept of the desiredstent.

As noted elsewhere, in one very desirable variation of the stent, asdeployed in FIGS. 2 and 3, the stent is folded longitudinally and isdelivered through the lumen of the catheter in such a way that it isself-restoring once it has been introduced to the selected body lumensite.

With that preliminary background in place, it should be apparent that asimple tube of metal will undergo plastic deformation when sufficientforce is applied radially to the outside of the tube. The amount offorce needed to cause that plastic deformation will depend on a widevariety of factors, e.g., the type of metal utilized in the tube, thewidth of the tube, the circumference of the tube, the thickness of thematerial making up the band, etc. The act of attempting to fold a tubealong its centered axis in such a way to allow it to pass through alumen having the same or smaller diameter and yet maintain the axis ofthe folded stent parallel to the axis of the lumen-invites plasticdeformation in and of the stent.

The described stent uses concepts which can be thought of as widelydistributing and storing the force necessary to fold the tubular stentinto a configuration which will fit through a diameter smaller than itsrelaxed outside diameter without inducing plastic deformation of theconstituent metal or plastic and yet allowing those distributed forcesto expand the stent upon deployment.

Once the concept of distributing the folding or compression stressesboth into a bending component (as typified by angle β° in FIG. 4) and totwisting components (as typified by angle γ° and δ° in FIG. 4), anddetermining the overall size of a desired stent, determination of theoptimum materials as well as the sizes of the various integralcomponents making up the stent becomes straightforward. Specifically,the diameter and length of torsion lengths (130 and 132) and end sector(104), the number of torsion pairs (102) around the stent may then bedetermined.

FIG. 5 shows, in side view, a variation of the stent (140) made fromwire having flares (142) at one or both ends. The flaring provides asecure anchoring of the stent or stent-graft (140) against the vesselwall. This prevents the implant from migrating downstream. In addition,the flaring provides a tight seal against the vessel so that the bloodis channelled through the lumen rather than outside the graft. Theundulating structure may vary in spacing to allow the helix turns tomaintain its phased relationship between turns of the helix and toconform to the discussion just above. A flexible linkage between thecontiguous helical turns may also be applied to at least a portion ofthe helices.

The stent structure may also be made by forming a desired structuralpattern out of a flat sheet. The sheet may then be rolled to form atube. FIGS. 6, 7, and 8 show plan views of torsion members (respectively200, 202, and 204) which may be then rolled about an axis (206) to forma cylinder. As is shown in FIG. 9, the end caps (208) may be aligned sothat they are "out of phase". The flexible linkage (210) is thenincluded to preserve the diameter of the stent.

The stent shown in FIG. 9 may be machined from tubing. If the chosenmaterial in nitinol, careful control of temperature during the machiningstep may be had by EDM (electro-discharge-machining), laser cutting,chemical machining, or high pressure water cutting.

FIG. 10 is a conceptual schematic of an isolated ring section of anothervariation of the stent component useful in this invention. The FIG. 10is intended only to identify and to provide conventions for naming thecomponents of the ring. FIG. 10 shows, in plan view, of the layout ofthe various components of a ring as if they were either to be cut from aflat sheet and later rolled into tubular formation for use as a stentwith welding or other suitable joining procedures taking place at theseam or (if constructed from tubing) the layout as if the tubing was cutopen. The portion of the stent between tie members (170) is designatedas a ring (172) or ring section. Tie members (170) serve to link onering (172) to an adjacent ring (172). A torsion pair (174) is made up ofa cap member (176) and two adjacent torsion members (178). Typically,then, each torsion member (178) will be a component to each of itsadjacent torsion pairs (174).

As ultimately deployed, a roll of the sheet found in FIG. 10 would beentered into the body lumen. Typically, it would be folded in somefashion which will be discussed below. A front quarter perspective viewof the rolled stent (178) is shown in the FIG. 11.

FIG. 12 shows a variation of the stent having a ring section (180)similar in configuration to that shown above and joined by tie members(182). Those tie members (182) extend from the inside of a torsion pair(184) to the outside of a torsion pair (186) in the adjacent ringsection. The tie members (182) experience no twisting because of theirplacement in the middle of end cap (188). The tie members may be offseton the end cap, if so desired, to allow the tie members to accept someof the twisting duty.

FIG. 13 shows a plan view of a variation of the inventive stent in whichthe number of torsion members (190) in a selected ring member (192) isfairly high. This added number of torsion members may be due to avariety of reasons. For instance, the material of construction may havea significantly lower tolerance for twisting than the materials in thoseprior Figures. Adding more torsion bars lessens the load carried on eachof the several bars. Alternatively, for the same material, the stent mayneed be folded to a smaller diameter for deployment than those earliervariations.

FIG. 14 shows a variation of the invention in which the end caps (194)are bound by a long torsion member (195) and two short torsion members(196). This torsion set (197) is in turn separated from the adjacenttorsion set (197) by a bridge member (198) which shares the bending loadof the stent when the stent is rolled and the ends (199) joined by,e.g., welding. The torsion members (196) have a greater width than thatof the long torsion member (195) so to balance the load around the ringduring deformation and thereby to prevent the bridge members frombecoming askew and out of the ring plane.

It should be clear that a variety of materials variously metallic,super-elastic alloys, and preferably nitinol, are suitable for use inthese stents. Primary requirements of the materials are that they besuitably springy even when fashioned into very thin sheets or smalldiameter wires. Various stainless steels which have been physically,chemically, and otherwise treated to produce high springiness aresuitable as are other metal alloys such as cobalt chrome alloys (e.g.,ELGILOY), platinum/tungsten alloys, various titanium alloys, andespecially the nickel-titanium alloys generically known as "nitinol".

Nitinol is especially preferred because of its "super-elastic" or"pseudo-elastic" shape recovery properties, i.e., the ability towithstand a significant amount of bending and flexing and yet return toits original form without deformation. These metals are characterized bytheir ability to be transformed from an austenitic crystal structure toa stress-induced martensitic structure at certain temperatures, and toreturn elastically to the austenitic shape when the stress is released.These alternating crystalline structures provide the alloy with itssuper-elastic properties. These alloys are well known but are describedin U.S. Pat. Nos. 3,174,851, 3,351,463, and 3,753,700. Typically,nitinol will be nominally 50.6% (±0.2%) Ni with the remainder Ti.Commercially available nitinol materials usually will be sequentiallymixed, cast, formed, and separately cold-worked to 30-40%, annealed, andstretched. Nominal ultimate yield strength values for commercial nitinolare in the range of 30 psi and for Young's modulus are about 700 kBar.

The '700 patent describes an alloy containing a higher iron content andconsequently has a higher modulus than the Ni--Ti alloys. Nitinol isfurther suitable because it has a relatively high strength to volumeratio. This allows the torsion members to be shorter than for lesselastic metals. The flexibility of the stent-graft is largely dictatedby the length of the torsion member components in the stent structuralcomponent. The shorter the pitch of the device, the more flexible thestent-graft structure can be made. Materials other than nitinol aresuitable. Spring tempered stainless steels and cobalt-chromium alloyssuch as ELGILOY are also suitable as are a wide variety of other known"super-elastic" alloys.

Although nitinol is preferred in this service because of its physicalproperties and its significant history in implantable medical devices,we also consider it also to be suitable for use as a stent because ofits overall suitability with magnetic resonance imaging (MRI)technology. Many other alloys, particularly those based on iron, are ananathema to the practice of MRI causing exceptionally poor images in theregion of the alloy implant. Nitinol does not cause such problems.

Other materials suitable as the stent include certain polymericmaterials, particularly engineering plastics such as thermotropic liquidcrystal polymers ("LCP's"). These polymers are high molecular weightmaterials which can exist in a so-called "liquid crystalline state"where the material has some of the properties of a liquid (in that itcan flow) but retains the long range molecular order of a crystal. Theterm "thermotropic" refers to the class of LCP's which are formed bytemperature adjustment. LCP's may be prepared from monomers such asp,p'-dihydroxy-polynuclear-aromatics or dicarboxy-polynuclear-aromatics.The LCP's are easily formed and retain the necessary interpolymerattraction at room temperature to act as high strength plastic artifactsas are needed as a foldable stent. They are particularly suitable whenaugmented or filled with fibers such as those of the metals or alloysdiscussed below. It is to be noted that the fibers need not be linearbut may have some preforming such as corrugations which add to thephysical torsion enhancing abilities of the composite.

The flexible linkage between adjacent turns of the helix (124 in FIGS. 2and 3) may be of any appropriate filamentary material which is bloodcompatible or biocompatible and sufficiently flexible to allow the stentto flex and not deform the stent upon folding. Although the linkage maybe a single or multiple strand wire (platinum, platinum/tungsten, gold,palladium, tantalum, stainless steel, etc.), much preferred is the useof polymeric biocompatible filaments. Synthetic polymers such aspolyethylene, polypropylene, polyurethane, polyglycolic acid,polyesters, polyamides, their mixtures, blends, copolymers, mixtures,blends and copolymers are suitable; preferred of this class arepolyesters such as polyethylene terephthalate including DACRON and MYLARand polyaramids such as KEVLAR, polyfluorocarbons such aspolytetrafluoroethylene with and without copolymerizedhexafluoropropylene (TEFLON or GORETEX), and porous or nonporouspolyurethanes. Natural materials or materials based on natural sourcessuch as collagen are especially preferred is this service.

Tubular Component

The tubular component or member of the stent-graft may be made up of anymaterial which is suitable for use as a graft in the chosen body lumen.For instance, natural material may be introduced onto the inner surfaceof the stent and fastened into place. Synthetic polymers such aspolyethylene, polypropylene, polyurethane, polyglycolic acid,polyesters, polyamides, their mixtures, blends, copolymers, mixtures,blends and copolymers are suitable; preferred of this class arepolyesters such as polyethylene terephthalate including DACRON and MYLARand polyaramids such as KEVLAR, polyfluorocarbons such aspolytetrafluoroethylene with and without copolymerizedhexafluoropropylene (TEFLON or GORETEX), and porous or nonporouspolyurethanes. Other especially preferred materials include the expandedfluorocarbon polymers (especially PTFE) materials described in British.Pat. Nos. 1,355,373, 1,506,432, or 1,506,432 or in U.S. Pat. Nos.3,953,566, 4,187,390, or 5,276,276, the entirety of which areincorporated by reference.

Collagen is easily formed into thin-walled tubes which are limp,compliant, flexible, uniform, and have smooth surfaces. The tubing wallsmay have a hydrated thickness of 0.001 to 0.020 inches (or to 0.100inches in some cases) for efficacy. Other thicknesses may be used ifspecific goals are to be achieved. They form non-thrombogenic surfaceswhich will support the growth of endothelium.

Highly preferred materials are certain collagen-based materials ofCOLLAGEN CORPORATION of Palo Alto, Calif. One such desired collagencomposition is a pharmaceutically acceptable non-immunogenic compositionformed by covalently binding atelopeptide collagen to pharmaceuticallypure, synthetic, hydrophilic polymers via specific types of chemicalbonds to provide collagen/polymer conjugates as is described in U.S.Pat. No. 5,162,430, to Rhee et al, and WO 94/01483 (PCT/US93/06292), theentirety of which are incorporated by reference.

Included in the class of preferred expanded fluoropolymers arepolytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP),copolymers of tetrafluoroethylene (TFE) and per fluoro(propyl vinylether) (PFA), homopolymers of polychlorotrifluoroethylene (PCTFE), andits copolymers with TFE, ethylene-chlorotrifluoroethylene (ECTFE),copolymers of ethylene-tetrafluoroethylene (ETFE), polyvinylidenefluoride (PVDF), and polyvinyfluoride (PVF). Especially preferred,because of its widespread use in vascular prostheses, is expanded PTFE.The graft may adhere to or partially encapsulate or be cast about thestent when appropriate materials such as castable polyurethane orcollagen-based materials are employed. When the stent-graft is producedin such a way that the openings in the stent contain graft material (asby casting), then we refer to such a stent-graft as an "integralstent-graft".

In a stent-graft, the graft tube acts as an intravascular blood conduitto line the interior surface of the blood vessel. It isolates the linedsegment of the vessel from direct contact with blood flow, tacks anytears or dissections, helps reinforce the vessel wall to protect againstor isolate aneurysms, and provides a smooth, relatively thin, conformalsurface for the blood flow.

The tubular component may be reinforced using a network of smalldiameter fibers. The fibers may be random, braided, roving, knitted, orwoven. The fibers may be imbedded in the tubular component wall, may beplaced in a separate layer coaxial with the tubular component, or may beused in a combination of the two.

The fibrous material may also be mixed with or imbedded into the tubularlayer and cast or injected around the stent. This fibrous material mayextend for the length of the device or may be shorter. The fibers may bewound or placed in any reasonable orientation within the device.Alternatively, randomly oriented short segments of fibers may also beimbedded in the wall of the tubing. The fiber may be any suitablefibrous blood-compatible material including polyesters such as DACRON,polyamides such as NYLON, KEVLAR, polyglycolic acids, polylactic acids,polyethylene, polypropylene, silk or other strong flexible fiber whichare not detrimentally affected in the medical service in which thisdevice is placed. Specifically, polypropylene and the like will not bedissolved in blood but polyglycolic acid will dissolve. Each aresuitable but work in different ways.

In addition, one or more radio-opaque metallic fibers, such as gold,platinum, platinum-tungsten, palladium, platinum-iridium, rhodium,tantalum, or alloys or composites of these metals like may beincorporated into the multi-strand reinforcement network to allowfluoroscopic visualization of the device.

In a polymer-fiber composite tube, the fibers carry much of the hoopstress and other loadings imposed by the vessel. This relieves theloading on the tube material, significantly increases the burst strengthand fatigue properties of the tube, and otherwise helps to provide asmoother wrinkle-free inner lumen. In addition, this makes the tube moreeffective in hydraulically isolating the vessel and as a result preventsthe formation or worsening of aneurysms. This would be particularlybeneficial in thinned weakened vessel walls resulting from de-bulkinginterventions or from medial thinning that has been seen to accompanystent placement. Another benefit of the fiber reinforcement is theincrease in resistance to radially inward loading, especially if theloading is very focussed. Finally, fiber reinforcement may also impartsome longitudinal stiffness to the stent-graft. This allows thestent-graft to maintain its strength and prevent it from kinking orsagging into the lumen.

Deployment of the Invention

When a stent-graft having torsion members is folded, crushed, orotherwise collapsed, mechanical energy is stored in torsion in thosetorsion members. In this loaded state, the torsion members have a torqueexerted about them and consequently have a tendency to untwist.Collectively, the torque exerted by the torsion members as folded downto a reduced diameter must be restrained from springing open. The stenttypically has at least one torsion member per fold to take advantage ofthe invention. The stent-graft is folded along its longitudinal axis andrestrained from springing open. The stent-graft is then deployed byremoving the restraining mechanism, thus allowing the torsion members tospring open against the vessel wall.

The attending surgeon will choose a stent or stent-graft having anappropriate diameter. However, inventive devices of this type aretypically selected having an expanded diameter of up to about 10%greater than the diameter of the lumen to be the site of the stentdeployment.

FIG. 15A shows a sequence of folding the device (230) of this inventionabout a guidewire (232) into a loose C-shaped configuration. FIG. 15Bshows a front quarter view of the resulting folded stent or stent-graft.

FIG. 15C shows a sequence of folding the device (230) of this inventionabout a guidewire (232) into a rolled configuration. FIG. 15D shows afront quarter view of the resulting folded stent or stent-graft.

FIG. 15E shows a sequence of folding the device (230) of this inventionabout a guidewire (232) into a triple lobed configuration. FIG. 15Fshows a front quarter view of the resulting folded stent or stent-graft.

The stent-graft may be tracked through the vasculature to the intendeddeployment site and then unfolded against the vessel lumen. The graftcomponent of the device, here depicted as a collagen tube, is limp,flexible, and thus easy to fold. Folding of the stent structure in themanner discussed above allows it to return to a circular, openconfiguration.

FIGS. 16A-16C show one desired way to place the devices of the presentinvention and allow them to self-expand. FIG. 16A shows a target site(246) having, e.g., a narrowed vessel lumen. A guidewire (248) having aguide tip (250) has been directed to the site using known techniques.The stent-graft (252) is mounted on guidewire tubing (254) inside outersliding sheath (256) after having folded in the manner discussed above.The outer sliding sheath (256) binds the compressed stent-graft (252) inplace until released.

FIG. 16B shows placement of the stent-graft (252) at the selected site(246) by sliding the stent-graft (252) over the guidewire (248) alltogether with the guidewire tubing (254) and the outer sliding sheath(256). The stent-graft (252) is deployed by holding the guidewire tubing(254) in a stationary position while withdrawing the outer slidingsheath (256). The stent-graft (252) can be seen in FIG. 16B as partiallydeployed.

FIG. 16C shows the stent-graft (252) fully deployed after the guidewiretubing (254) and the outer sliding sheath (256) have been fullyretracted.

FIGS. 17A-C, 18A-C, and 19A-C show an inventive variation of deploying astent or stent-graft made according to this invention. These methodsinvolve the use of a control line or tether line which maintains thestent or stent-graft in a folded configuration until release.

FIG. 17A is a front-quarter view of the stent (302) or stent-graft whichhas been folded as shown in the Figures discussed above. The stent (302)is folded about guidewire (304) so that, when deployed, the guidewire(304) is within the stent (302). Central to the variation shown here isthe tether wire (306) which is passed through loops (308) associatedwith the various helices as they wind about the stent (302). The loops(308) may be formed from the flexible link (124 in FIGS. 2 or 3) or maybe simply an alternating weave through (or adjacent to) appropriateapexes of the undulating helix, e.g., (104 in FIG. 3) or may be loopsspecifically installed for the purpose shown here. It should be clearthat the tether wire (306) is so placed that when it is removed bysliding it axially along the stent (302) and out of the loops (308),that the stent (302) unfolds into a generally cylindrical shape withinthe body lumen or cavity.

FIG. 17B shows an end-view of a folded stent (302) or stent-graft havinga guidewire (304) within the inner surface of the stent (302) and withthe tether wire (306) within the loops (308). The end view of the foldedstent (302) shows it to be folded into a form which is generallyC-shaped. When expanded by removal of the tether wire (306), the stent(302) in FIG. 17B assumes the form shown in end view in FIG. 17C. Theremay be seen the guidewire (304) within the lumen of the stent (302) andthe loops (308) which were formerly in a generally linear relationshiphaving a tether wire passing through them.

FIG. 18A shows a folded stent (310) (or stent-graft) in front quarterview which is similar in configuration to the stent (302) shown in FIG.17A except that the stent (310) is rolled somewhat tighter than thepreviously discussed stent. The guidewire (304) is also inside the stent(310) rather than outside of it. Loops (308) from generally opposingsides of the stent (310) are folded into an approximate line so that thetether wire may pass through the aligned loops (308). FIG. 18B shows anend view of the stent (310), and in particular, emphasizes the tighterfold of the stent (310). When expanded by removal of the tether wire(306), the stent (310) in FIG. 18B assumes the form shown in FIG. 18C.In FIG. 18C may be seen the guidewire (304) within the lumen of thestent (310) and the loops (308) which were formerly in a generallylinear relationship having a tether wire passing through them.

FIGS. 19A-C show an additional schematic procedure for deploying thestent (312) (or stent-graft) using a percutaneous catheter assembly(314).

In FIG. 19A may be seen a percutaneous catheter assembly (314) which hasbeen inserted to a selected site (316) within a body lumen. The stent(312) is folded about the guidewire (319) and guidewire tube (318) heldaxially in place prior to deployment by distal barrier (320) andproximal barrier (322). The distal barrier (320) and proximal barrier(322) typically are affixed to the guidewire tube (318). The tether wire(306) is shown extending through loops (308) proximally through thecatheter assembly's (314) outer jacket (324) through to outside thebody.

FIG. 19B shows the removal of the tether wire (306) from a portion ofthe loops (308) to partially expand the stent (312) onto the selectedsite (316).

FIG. 19C shows the final removal of the tether wire (306) from the loops(308) and the retraction of the catheter assembly (314) from theinterior of the stent (312). The stent (312) is shown as fully expanded.

FIG. 20 shows a close-up of a stent fold line having the familiarherringbone pattern of the "sack knot" used to close the fold in thestent. This knot is the one used to hold, e.g., burlap sacks of feedgrain closed prior to use and yet allow ease of opening when the sack isto be opened. In this variation, the slip line has a fixed end (320) anda release end (322). loops of the slip line pass through the eyelets(324) on the side of the stent fold associated with the fixed end (320)and are held in place by eyelets (326) on the side of the stent foldassociated with the release end (322). The fixed end (320) is nottypically tied to the stent so to allow removal of the slip line afterdeployment. The eyelets (324 and 326) are desirable but optional. Theeyelets (324 and 326) may be wire or polymeric thread or the like tiedto the stent structure at the edge of the stent fold. If so desired, theloops may be dispensed with and the slip line woven directly into thestent structure. The self-expanding stent may be deployed by pullingaxially on release end (322) as shown by the arrow in the drawing.

FIGS. 21 and 22 show front quarter views of folded stents using the knotshown in FIG. 20. FIG. 21 shows the use of a single stent fold similarin configuration to those described above. As was shown in FIG. 20, thefixed end (320) portion of the slip line is associated with a row ofeyelets (324) which are tied or otherwise fixed to the stent. Therelease end (322) is associated with the other row of eyelets (326).

FIG. 22 merely depicts the use of multiple stent folds each having afixed end (320 & 330) and a release end (322 & 332) on their respectiveslip lines.

The variations of the invention shown in FIGS. 20-22 may be introducedin to the body using the procedures outlined above with relation toFIGS. 15-19.

Although we generally discuss the deployment of the stent or stent-graftusing a catheter, often deployed percutaneously, it should be apparentthat the procedure and the folded stent or stent-graft are not solimited. The folded stent or stent-graft may also be deployed throughartificial or natural body openings with a sheath or endoscopic deliverydevice perhaps without a guidewire. Similarly, the stent or stent graftmay be delivered manually during a surgical procedure.

Many alterations and modifications may be made by those of ordinaryskill in the art without departing from the spirit and scope of theinvention. The illustrated embodiments have been shown only for purposesof clarity and examples, and should not be taken as limiting theinvention as defined by the following claims, which include allequivalents, whether now or later devised.

We claim as our invention:
 1. A method for introducing a self-expandingstent into a lumen comprising:providing a self-expanding stent in alongitudinally folded configuration and maintained in said foldedconfiguration by a removable, longitudinally positioned slip lineattached along a longitudinal fold line of said folded configuration;introducing said folded self-expanding stent to a selected site in alumen; and axially withdrawing said slip line in a directionsubstantially aligned with a longitudinal axis of said self-expandingstent, thereby releasing said slip line to allow the stent to expand atthe selected site.
 2. The method of claim 1 in which the selected siteis a vascular site.
 3. The method of claim 1 in which the self-expandingstent further comprises loops along said fold line in the stent throughwhich the slip line is introduced.
 4. The method of claim 1 in which theremovable slip line is woven into the stent at a fold line using a sackknot so to allow removal of the slip line by unweaving the sack knotthrough axial movement of the slip line.
 5. The method of claim 1 inwhich the stent is metallic.
 6. The method claim 1 in which the stentfurther comprises a super-elastic alloy.
 7. The method of claim 1 inwhich the stent further comprises a nickel-titanium alloy.
 8. The methodof claim 1 where the stent further comprises a helically positionedundulating member which forms multiple turns about a longitudinal axisof said stent.
 9. The method of claim 8, where said undulating memberincludes undulations and a flexible link passes through undulations onadjacent helical turns of said undulating member.
 10. The method ofclaim 9 where said flexible link maintains said undulations in phasedrelationship between said adjacent helical turns.
 11. The method ofclaim 1 further comprising a graft attached to the stent.
 12. The methodof claim 11 in which the graft is a polymeric material.
 13. The methodof claim 11 where the graft comprises a tubular member.
 14. The methodof claim 11 where the graft comprises a tubular member includingradiopaque markers.
 15. The method of claim 11 in which the graftcomprises a polyethylene terephthalate material.
 16. The method of claim11 in which the graft comprises a polyaramid material.
 17. The method ofclaim 11 in which the graft comprises a polyfluorocarbon material. 18.The method of claim 11 in which the graft comprises a polyurethane. 19.A method for introducing a self-expanding stent into a lumencomprising:providing a self-expanding stent in a folded configurationand maintained in said folded configuration by a removable,longitudinally positioned slip line woven along a longitudinal fold lineof said folded configuration using a sack knot; introducing said foldedself-expanding stent to a selected site in a lumen; and axiallywithdrawing said slip line in a direction substantially aligned with alongitudinal axis of said self-expanding stent, thereby unweaving saidslip line to allow the stent to expand at the selected site.
 20. Amethod for introducing a self-expanding stent-graft into a lumencomprising:providing a self-expanding stent-graft in a foldedconfiguration and maintained in said folded configuration by aremovable, longitudinally positioned slip line woven along alongitudinal fold line of said folded configuration using a sack knot;introducing said folded self-expanding stent to a selected site in alumen; and axially withdrawing said slip line in a directionsubstantially aligned with a longitudinal axis of said self-expandingstent, thereby unweaving said slip line to allow the stent to expand atthe selected site.
 21. The method of claim 20 in which the graftcomprises a polyfluorocarbon material.
 22. The method of claim 21 inwhich the polyfluorocarbon material comprises expandedpolytetrafluoroethylene.